Effect of Iron Complex Source on MWWTP Effluent Treatment by Solar Photo-Fenton: Micropollutant Degradation, Toxicity Removal and Operating Costs.

Benzophenone-3, fipronil and propylparaben are micropollutants that are potential threats to ecosystems and have been detected in aquatic environments. However, studies involving the investigation of new technologies aiming at their elimination from these matrices, such as advanced oxidation processes, remain scarce. In this study, different iron complexes (FeCit, FeEDTA, FeEDDS and FeNTA) were evaluated for the degradation of a mixture of these micropollutants (100 µg L−1 each) spiked in municipal wastewater treatment plant (MWWTP) effluent at pH 6.9 by solar photo-Fenton. Operational parameters (iron and H2O2 concentration and Fe/L molar ratio) were optimized for each complex. Degradation efficiencies improved significantly by increasing the concentration of iron complexes (1:1 Fe/L) from 12.5 to 100 µmol L−1 for FeEDDS, FeEDTA and FeNTA. The maximum degradation reached with FeCit for all iron concentrations was limited to 30%. Different Fe/L molar ratios were required to maximize the degradation efficiency for each ligand: 1:1 for FeNTA and FeEDTA, 1:3 for FeEDDS and 1:5 for FeCit. Considering the best Fe/L molar ratios, higher degradation rates were reached using 5.9 mmol L−1 H2O2 for FeNTA and FeEDTA compared to 1.5 and 2.9 mmol L−1 H2O2 for FeEDDS and FeCit, respectively. Acute toxicity to Canton S. strain D. melanogaster flies reduced significantly after treatment for all iron complexes, indicating the formation of low-toxicity by-products. FeNTA was considered the best iron complex source in terms of the kinetic constant (0.10 > 0.063 > 0.051 > 0.036 min−1 for FeCit, FeNTA, FeEDTA and FeEDDS, respectively), organic carbon input and cost-benefit (USD 327 m−3 > USD 20 m−3 > USD 16 m−3 > USD 13 m−3 for FeEDDS, FeCit, FeEDTA and FeNTA, respectively) when compared to the other tested complexes.

Degradation mechanism of fipronil and its transformation products, matrix effects and toxicity during the solar/photo-Fenton process using ferric citrate complex.

This study presents the degradation of fipronil in sewage treatment plant (STP) effluent by photo-Fenton at near neutral pH (pH 6.0) using Fe3+/Citrate complex. 83% of fipronil degradation was reached using a molar iron/citrate ratio of 1:3 (192 µmol L-1 of Fe3+/576 µmol L-1 of citrate). Photo-Fenton reduced the toxicity of treated solutions as according to the survival of Drosophila melanogaster exposed to non-treated and treated samples. Control experiments performed in distilled water using 32 µmol L-1 of Fe3+/96 µmol L-1 of citrate achieved 98% of fipronil degradation within 100 kJ m-2 (UV-A radiation, k = 30 × 10-3 kJ-1 m2 and t1/2 = 23 kJ m-2), thus indicating that fipronil degradation is impaired by natural organic matter and inorganic ions present in STP effluent. Degradation was faster under solar radiation, as the same efficiency (98%) was obtained after 75 kJ m-2 (k = 63 × 10-3 kJ-1 m2 and t1/2 = 11 kJ m-2). In addition, pathways of fipronil degradation using Fe3+/Citrate under solar and UV-A radiation were investigated and transformation products proposed. Results revealed that the HO• attack occurred preferentially in the pyrazole ring. Eight transformation products were identified by UHPLC-Q-TOF-MS and four are unprecedented in the literature. Control experiments in distilled water demonstrated that toxicity reduction is related to fipronil degradation and that transformation products are less toxic than fipronil. Furthermore, toxicity of STP fortified with fipronil was reduced after photo-Fenton. These results demonstrate the feasibility of applying this process using Fe3+/Citrate complex for fipronil degradation in a real matrix.

Design of an industrial solid waste processing line to produce refuse-derived fuel.

Municipal Solid Waste (MSW) from the city of Boa Esperança, Minas Gerais, Brazil, was used to produce refuse-derived fuel (RDF). The MSW contains residues from human society, including product packaging, bottles, batteries, organic waste, fines, textiles, health textiles, plastics, glass, and metals, among others. The following protocol was performed during the conversion of MSW to RDF: (i) the raw MSW was placed in a silo and sent to a primary crusher using a metal conveyor belt, which reduced the particle size to 80 mm; (ii) the biomass was transferred to a selective waste collection platform by a rubber conveyor belt, and the recyclable waste, metals, and glasses were separated manually; (iii) residual metals were removed by a magnetic separator; (iv) the waste was transferred to a secondary crusher which reduced the particle size to 60 mm; (v) the waste passed through an airborne separator to remove materials with high density, such as glass, stones, and organic materials, using a metallic conveyor belt; (vi) the particle size was reduced to 40 mm by a tertiary crusher; (vii) the aluminium was separated from the non-metallic materials (plastic, paper, rubber, etc.) using an eddy current separator; (viii) the particle size was reduced to 25 mm using a quaternary crusher; (ix) the MSW was introduced into a rotary dryer using a metal conveyor belt, where the moisture content was reduced to close to 15 wt%, which required thermal energy equivalent to 186 kWh; (x) the RDF was used in a thermochemical reactor and 4148 kWh of thermal energy was produced. In addition, the MSW and RDF were analysed, and the elemental composition and combustion characteristics were determined. Based on these results, the protocol evaluated was found to be effective in the conversion of MSW to RDF, which can be used as a source of renewable fuel.

Correlation between pH and molar iron/ligand ratio during ciprofloxacin degradation by photo-Fenton process: Identification of the main transformation products.

Ciprofloxacin has been determined with high frequency in studies involving environmental waters matrixes. However, no study evaluating the correlation between the initial pH and molar iron/organic ligand ratio has been published. This paper describes the degradation of the antibiotic ciprofloxacin by the photo-Fenton process using different sources of iron (Fe2+, Fe3+ and Fe3+-citrate and Fe3+-oxalate, named FeCit and FeOx, respectively) and molar iron/organic ligand ratios at initial pH values of 2.5 and 6.5. The best results at initial pH 2.5 were achieved using FeCit and FeOx at molar iron/organic ligand ratios of 1:1 and 1:3 respectively, when the ciprofloxacin concentration reached values below the quantitation limit of the HPLC after 20 min of treatment. However, at initial pH 6.5, improvements in the results (15% for FeCit, and 46% for FeOx) were achieved by increasing the molar iron/organic ligand ratios to 1:4 (FeCit) and 1:9 (FeOx), respectively. Three transformation products, (C17H19FN3O4, m/z 348; C17H21FN3O5, m/z 366; and C13H12FN2O3, m/z 263) of ciprofloxacin degradation were identified, one of them not yet being reported in the literature (C17H21FN3O5, m/z 366). Their formation and degradation was monitored and the initial steps of their formation and degradation were proposed. The results show that the piperazine ring is more susceptible to hydroxyl radical attack than the quinolone ring, which persists in the intermediates identified. Therefore, this process can be a good alternative for the treatment of this type of pollutant at near-neutral conditions.

Integrating coagulation-flocculation and UV-C or H2O2/UV-C as alternatives for pre- or complete treatment of biodiesel effluents.

The feasibility of biodiesel effluent treatment combining coagulation-flocculation with a photolytic process was evaluated, being the photolytic process involving the irradiation of the effluent by UV-C, or by UV-C irradiation with simultaneous addition of H2O2 (H2O2/UV-C). The coagulation-flocculation was performed at the natural pH of the effluent (pH 2.9) using different Fe3+ salts (chloride, nitrate and sulfate) at different concentrations (0.25, 0.50 and 1.0 mmol L-1) of the counterions. The best results were achieved using 0.50 mmol L-1 Fe(NO3)3. Following, the degradation of the organic load and toxicity reduction of the pre-treated effluent by UV-C irradiation was evaluated. The H2O2/UV-C process showed to be advantageous, mainly when multiple additions of H2O2 were used during the course of the reaction. Additionally, the influence of the initial pH on the degradation was also evaluated. A high level of mineralization (94%) was achieved after 6 h of irradiation concomitantly with multiple additions of 2,000 mg L-1 H2O2, and with the effluent at the natural pH. Thus, using coagulation-flocculation followed by the H2O2/UV-C process, it was possible to achieve a favourable condition for reuse of the pre-treated effluent, since, in addition to the significant reduction of the organic load, the final DBO5 (<120 mg L-1) and oils & fats (<50 mg L-1) are below the limits established by the Brazilian legislation. Furthermore, a reduction of 78% of acute toxicity to V. fischeri (from 89% to 20%) was reached. The results suggest, therefore, that this process is a viable option for treatment of this kind of effluent.

Enhancing disinfection and microcontaminant removal by coupling LED driven UVC and UVA/photo-Fenton processes in continuous flow reactors.

For the first time, the sequential combination of UVC-LED (276 nm) and photo-Fenton/UVA-LED (376 nm) process has been assessed in continuous flow mode for wastewater reclamation according to the new European Regulation for reuse in agricultural irrigation (EU 2020/741). The results show that it is possible to obtain water quality class B (Escherichia coli ≤ 100 CFU/100 mL) by UVC-LED irradiation alone, operating the system with a hydraulic residence time (HRT) of 6.5 min and liquid depth of 5 cm in the case of secondary effluents with low Escherichia coli load (8.102-3.1.103 CFU/100 mL). As for high bacteria concentrations (1.2-4.2.104 CFU/100 mL), HRTs longer than 30 min are required. The bacterial load has not influenced decontamination, removing 18 ± 4 % of microcontaminants. Coupling the UVC (30-min HRT and 5.0 cm liquid depth) and the UVA/photo-Fenton (60-min and 15-cm liquid depth) systems allows 58 ± 4 % of real organic microcontaminants to be removed, in addition to achieving water quality class B.

Influence of water matrix components and peroxide sources on the transformation products and toxicity of tebuthiuron under UVC-based advanced oxidation processes.

Coupling of UV-C irradiation to different peroxides (H2O2, S2O82- and HSO5-) has great potential to degrade persistent organic compounds due to the formation of HO• or SO4•- species. However, an in-depth comparison between the performance of different UV-C/peroxide processes as a function of (i) target compound degradation, (ii) generated transformation products and (iii) lethal/sub lethal toxicity effects has not yet been performed. To this end a comparison study was carried out to evaluate the effectiveness of different UV-C/peroxide processes using the herbicide tebuthiuron (100 or 500 µg L-1) as a model pollutant. TBH degradation experiments were performed at lab-scale in real municipal wastewater treatment plant effluent and distilled water. Faster degradation occurred by increasing peroxide concentration from 735 to 2206 µmol L-1 in the municipal wastewater treatment plant effluent, mainly for S2O82-. Experiments performed in the presence of peroxide trapping agents - HO• and SO4•- (methoxibenzene) or HO• (2-propanol) - revealed that oxidation in the UV-C/S2O82- system occurs mainly through SO4•-. Lower toxicity for the MWWTP effluent was obtained after oxidative treatments using hydrogen peroxide or monopersulfate as oxidants which react mainly through HO• radicals. Two mechanistic pathways were proposed for tebuthiuron degradation: (i) hydrogen abstraction by HO• (H2O2 and HSO5-) and (ii) electron transfer by SO4•- (S2O82-). In addition, one unprecedented transformation product was identified. In conclusion, results emphasize the relevance of comparing the degradation of toxic compounds in the presence of different peroxide sources and matrices and simultaneouly evaluating responses chemical and biological endpoints.

A review toward contaminants of emerging concern in Brazil: Occurrence, impact and their degradation by advanced oxidation process in aquatic matrices.

This work presents data regarding the occurrence and treatment of Contaminants of Emerging Concern (CECs) in Brazil in the past decade. The literature review (2011-2021) revealed the detection of 87 pharmaceutical drugs and personal care products, 58 pesticides, 8 hormones, 2 illicit drugs, caffeine and bisphenol A in distinct matrices (i.e.: wastewater, groundwater, sea water, rainwater, surface water, drinking water and hospital effluent). Concentrations of CECs varied from ng-µg L-1 depending on the location, compound and matrix. The inefficiency of conventional wastewater treatment methods on the removal of CECs and lack of basic sanitation in some regions in the country aggravates contamination of Brazilian aquatic environments and poses potential environmental and health risks. Advanced oxidation processes (AOPs) are pointed out as viable and efficient alternatives to degrade CECs and prevent environmental contamination. A total of 375 studies involving the use of AOPs in Brazilian aqueous matrices were published in the last decade. Fenton and photo-Fenton processes, photo-peroxidation, ozonation, electrochemical advanced oxidation and heterogeneous photocatalysis are some of the AOPs applied by Brazilian research groups. Although many works discuss the importance of applying these technologies for CECs removal in real treatment plants, most of these studies assess the treatment of distilled water or simulated effluent. Therefore, the conduction of studies applying AOPs in real matrices are critical to drive the implementation of these processes coupled to conventional water and wastewater treatment in real plants in order to prevent the contamination of environmental matrices by CECs in Brazil.

Chemical and toxicological evaluation along with unprecedented transformation products during photolysis and heterogeneous photocatalysis of chloramphenicol in different aqueous matrices.

As the presence of antibiotics in environmental waters enhances antimicrobial resistance, photolysis and heterogeneous photocatalysis of chloramphenicol (CAP) were evaluated in deionized water (DW) and in sewage treatment plant (STP) effluent under black light and solar irradiation. Processes were compared in terms of CAP degradation, reaction kinetics, and electrical energy per order, as well as regarding theoretical toxicity, biodegradability, carcinogenicity, and mutagenicity of transformation products (TPs). Rate constants obtained under photolysis (0.008 min-1) and heterogeneous photocatalysis (0.18 min-1) only differed in DW. This is due to the generation of photo-active reactive oxygen species (HO· and HO2·-/O2·-) under photolysis in STP effluent, as verified by experiments in the presence of 2-propanol and chloroform. Natural organic matter and HCO3- were the main responsible for reducing CAP degradation in STP effluent. Fifteen TPs were identified during both processes in DW, 13 of which are unprecedented. TPs were formed mainly via HO· preferential attack on the aromatic ring and on the α-carbon, and some of them were classified as persistent and toxic, genotoxic, or carcinogenic by Toxtree software. Results confirm that solar photocatalysis is less costly than to photocatalysis under black light for wastewater treatment.

Reducing toxicity and antimicrobial activity of a pesticide mixture via photo-Fenton in different aqueous matrices using iron complexes.

This is the first study to investigate ethylenediamine-N,N'-disuccinic acid (EDDS)/photo-Fenton process to polish real wastewater containing pesticides for possible water reuse. To this end, simultaneous degradation of pesticides ametrine, atrazine, imidacloprid and tebuthiuron was evaluated in distilled water (DW) and in sewage treatment plant (STP) effluent at initial pH 6.0. Several operational parameters (Fe3+-EDDS concentration, Fe3+-EDDS molar ratio, EDDS addition patterns and radiation source) were evaluated. 80-98% removal of target pesticides were obtained in DW using 30 µmol L-1 of Fe3+-EDDS with a molar ratio of 1:2 (300 µmol L-1 of H2O2). In addition, the proposed Fe3+-EDDS photo-Fenton at pH 6 was more efficient than classic photo-Fenton at pH 2.7 (30-84% removal). Experiments conducted in the presence of radical trapping agents (2-propanol or chloroform) revealed that HO• was the most active radical during treatment. Matrix composition strongly affected the degradation of target pesticides as a six-fold higher concentration of reagents (180 µmol L-1 of Fe3+-EDDS and 1800 µmol L-1 of H2O2) was needed to reach the same efficiency in STP compared to DW. Even so, first order rate constants corresponding to the degradation of pesticides in DW (k = 0.098-0.85 min-1) were nearly two-fold higher than in STP (k = 0.079-0.49 min-1) under the same radiation source (black-light or solar radiation). Finally, acute toxicity towards Vibrio fischeri and Drosophila melanogaster flies, and antibacterial activity assessed for Escherichia coli were eliminated after the application of the proposed treatment, thus indicating environmental safety for either discharge or reuse of treated wastewater for crop irrigation in agriculture.

Environmental implications of soil remediation using the Fenton process.

This work evaluates some collateral effects caused by the application of the Fenton process to 1,1-bis(4-chlorophenyl)-2,2,2-trichloroethane (DDT) and diesel degradation in soil. While about 80% of the diesel and 75% of the DDT present in the soil were degraded in a slurry system, the dissolved organic carbon (DOC) in the slurry filtrate increased from 80 to 880mgl(-1) after 64h of reaction and the DDT concentration increased from 12 to 50microgl(-1). Experiments of diesel degradation conducted on silica evidenced that soluble compounds were also formed during diesel oxidation. Furthermore, significant increase in metal concentrations was also observed in the slurry filtrate after the Fenton treatment when compared to the control experiment leading to excessive concentrations of Cr, Ni, Cu and Mn according to the limits imposed for water. Moreover, 80% of the organic matter naturally present in the soil was degraded and a drastic volatilization of DDT and 2,2-bis(4-chlorophenyl)-1,1-dichloroethylene was observed. Despite the high percentages of diesel and DDT degradation in soil, the potential overall benefits of its application must be evaluated beforehand taking into account the metal and target compounds dissolution and the volatilization of contaminants when the process is applied.

Optimization of fipronil degradation by heterogeneous photocatalysis: Identification of transformation products and toxicity assessment.

In this work it was studied the degradation of the insecticide fipronil (FIP) by heterogeneous photocatalysis induced by TiO2 P25. Using chemometric methods (Factorial Design and Response Surface Methodology), it was possible to evaluate the role of interaction between pH of the reaction medium, the reaction time and concentration of TiO2, optimizing the conditions for degradation using artificial radiation. Under the optimized conditions (79.4 mg L-1 TiO2 and 66.3 min of reaction time for 1.1 mg L-1 of FIP, at pH 5.6-5.8 (natural pH of the irradiated suspension)), 90.9% of FIP degradation was achieved at a degradation rate of 1.54 × 10-2 m2 kJ-1 in terms of accumulated UVA radiation, corresponding to a pseudo-first order rate constant of 1.34 × 10-2 min-1 and a half-life of 51.7 min. Under the same conditions, these assays were extended to the use of solar radiation, when the degradation rate was 14% higher, with half-life of 45 min, suggesting that in both cases FIP degradation was successful. Four by-products of FIP photocatalytic degradation could be separated, identified, and their formation and consumption followed by UHPLC-Q-TOF. Although the same intermediates have been obtained using both irradiation sources, a faster degradation of the transformation products (TPs) was observed under solar irradiation due to its expressive photonic flux covering the UVA and UVB. It is noteworthy that both the untreated effluent and the identified compounds have low toxicity with respect to V. fischeri, suggesting that the heterogeneous photocatalysis may be a good alternative for treatment of wastewaters containing FIP and its TPs, mainly when solar radiation is the source of radiation, since under this condition the power consumption during the treatment can be significantly reduced.

Degradation of Direct Red 81 mediated by Fenton reactions: multivariate optimization, effect of chloride and sulfate, and acute ecotoxicity assessment.

The role of different operational parameters related to Fenton reactions (pH, concentration of Fe2+ and H2O2, and reaction time) and of Cl- and SO 4- was investigated in the degradation of the azo dye Direct Red 81, expressed in terms of its decolorization. The factorial design and Pareto's charts showed that only Fe2+ concentration and pH influence the decolorization under the conditions evaluated. So, only these parameters were optimized using the response surface model. Under the best experimental conditions (initial pH 2.5, 11 mg L-1 Fe2+, 78 mg L-1 H2O2, and 20 min of reaction), 94 % of decolorization was achieved. However, even under the these conditions, but in the presence of Cl- and SO 4- , a striking loss of efficiency was observed as the concentration of these ions was increased, due the formation of chloride- and sulfate-iron complexes and less reactive inorganic radicals (Cl2•- and SO4•-). The results show that the presence of Cl- is more deleterious, since sulfate-iron complexes are more reactive towards H2O2, and the SO4•- turns out to favor the degradation. On the other hand, the  negative effect of Cl- can be compensated by increasing the chloride concentration up to 300 mmol L-1. In addition, although a high degradation level has been obtained by monitoring the dye absorbance and by HPLC-UV, a low mineralization occurred, being generated degradation products of higher ecotoxicity to Vibrio fischeri, showing the need of subsequent studies to identify these compounds as well as the application of additional treatments aiming the complete mineralization of the dye.

Evaluation of the influences of solution path length and additives concentrations on the solar photo-Fenton degradation of 4-chlorophenol using multivariate analysis.

This study reports the photodegradation of 4-chlorophenol (4-CP) in aqueous solution by the photo-Fenton process using solar irradiation. The influence of solution path length, and Fe(NO(3))(3) and H(2)O(2) concentrations on the degradation of 4-CP is evaluated by response surface methodology. The degradation process was monitored by the removal of total organic carbon (TOC) and the release of chloride ion. The results showed a very important role of iron concentration either for TOC removal or dechlorination. On the other hand, a negative effect of increasing solution path length on mineralization was observed, which can be compensated by increasing the iron concentration. This permits an adjustment of the iron concentration according to the irradiation exposure area and path length (depth of a tank reactor). Under optimum conditions of 1.5 mM Fe(NO(3))(3), 20.0 mM H(2)O(2) and 4.5 cm solution path length, 17 min irradiation under solar light were sufficient to reduce a 72 mg CL(-1) solution of 4-CP by 91%.

Solar photodegradation of dichloroacetic acid and 2,4-dichlorophenol using an enhanced photo-Fenton process.

The photo-Fenton process using potassium ferrioxalate as a mediator was investigated for the photodegradation of dichloracetic acid (DCA) and 2,4-dichlorophenol (DCP) in aqueous medium using solar light as source of irradiation. The influence of the solution depth, the light intensity and the effect of stirring the solution during irradiation process were evaluated using DCA as a model compound. A negligible influence of stirring the solution was observed when the concentration of ferrioxalate (FeOx) was 0.8 mM and solution depth was 4.5 or 14 cm. The optimum FeOx concentration determined for solution depths between 4.5 and 14 cm was 0.8 mM considering total organic carbon (TOC) removal during DCA irradiation. The high efficiency of the photo-Fenton process was demonstrated on summer days, when only 10 min of exposition (around noon) were sufficient to completely destroy the organic carbon of a 1.0 mM DCA solution in the presence of 0.8 mM FeOx and 6.0 mM H2O2 using a solution depth of 4.5 cm. It was observed that the photodegradation efficiency increases linearly with the solar light intensity up to values around 15 Wm(-2) but this linear relationship does not hold above this value showing a square root dependence. The photodegradation of a solution of DCP/FeOx showed a lower TOC removal rate than that observed for DCA/FeOx, achieving approximately 90% after 35 min irradiation under 19 W m(-2), while under this light intensity, the same TOC removal of DCA/FeOx was achieved in only 10 min irradiation.

Degradation of caffeine by photo-Fenton process: optimization of treatment conditions using experimental design.

The degradation of caffeine in different kind of effluents, via photo-Fenton process, was investigated in lab-scale and in a solar pilot plant. The treatment conditions (caffeine, Fe(2+) and H(2)O(2) concentrations) were defined by experimental design. The optimized conditions for each variable, obtained using the response factor (% mineralization), were: 52.0 mg L(-1)caffeine, 10.0 mg L(-1)Fe(2+) and 42.0 mg L(-1)H(2)O(2) (replaced in kinetic experiments). Under these conditions, in ultrapure water (UW), the caffeine concentration reached the quantitation limit (0.76 mg L(-1)) after 20 min, and 78% of mineralization was obtained respectively after 120 min of reaction. Using the same conditions, the matrix influence (surface water - SW and sewage treatment plant effluent - STP) on caffeine degradation was also evaluated. The total removal of caffeine in SW was reached at the same time in UW (after 20 min), while 40 min were necessary in STP. Although lower mineralization rates were verified for high organic load, under the same operational conditions, less H(2)O(2) was necessary to mineralize the dissolved organic carbon as the initial organic load increases. A high efficiency of the photo-Fenton process was also observed in caffeine degradation by solar photocatalysis using a CPC reactor, as well as intermediates of low toxicity, demonstrating that photo-Fenton process can be a viable alternative for caffeine removal in wastewater.

Paracetamol degradation intermediates and toxicity during photo-Fenton treatment using different iron species.

The photo-Fenton degradation of paracetamol (PCT) was evaluated using FeSO(4) and the iron complex potassium ferrioxalate (FeOx) as iron source under simulated solar light. The efficiency of the degradation process was evaluated considering the decay of PCT and total organic carbon concentration and the generation of carboxylic acids, ammonium and nitrate, expressed as total nitrogen. The results showed that the degradation was favored in the presence of FeSO(4) in relation to FeOx. The higher concentration of hydroxylated intermediates generated in the presence of FeSO(4) in relation to FeOx probably enhanced the reduction of Fe(III) to Fe(II) improving the degradation efficiency. The degradation products were determined using liquid chromatography electrospray time-of-flight mass spectrometry. Although at different concentrations, the same intermediates were generated using either FeSO(4) or FeOx, which were mainly products of hydroxylation reactions and acetamide. The toxicity of the sample for Vibrio fischeri and Daphnia magna decreased from 100% to less than 40% during photo-Fenton treatment in the presence of both iron species, except for D. magna in the presence of FeOx due to the toxicity of oxalate to this organism. The considerable decrease of the sample toxicity during photo-Fenton treatment using FeSO(4) indicates a safe application of the process for the removal of this pharmaceutical.

Degradation of the antibiotic amoxicillin by photo-Fenton process--chemical and toxicological assessment.

The influence of iron species on amoxicillin (AMX) degradation, intermediate products generated and toxicity during the photo-Fenton process using a solar simulator were evaluated in this work. The AMX degradation was favored in the presence of the potassium ferrioxalate complex (FeOx) when compared to FeSO(4). Total oxidation of AMX in the presence of FeOx was obtained after 5 min, while 15 min were necessary using FeSO(4). The results obtained with Daphnia magna biossays showed that the toxicity decreased from 65 to 5% after 90 min of irradiation in the presence of FeSO(4). However, it increased again to a maximum of 100% after 150 min, what indicates the generation of more toxic intermediates than AMX, reaching 45% after 240 min. However, using FeOx, the inhibition of mobility varied between 100 and 70% during treatment, probably due to the presence of oxalate, which is toxic to the neonates. After 240 min, between 73 and 81% TOC removal was observed. Different pathways of AMX degradation were suggested including the opening of the four-membered ß-lactamic ring and further oxidations of the methyl group to aldehyde and/or hydroxylation of the benzoic ring, generating other intermediates after bound cleavage between different atoms and further oxidation to carboxylates such acetate, oxalate and propionate, besides the generation of nitrate and ammonium.

Soil remediation using a coupled process: soil washing with surfactant followed by photo-Fenton oxidation.

In the present work the use of a coupled process, soil washing and photo-Fenton oxidation, was investigated for remediation of a soil contaminated with p,p'-DDT (DDT) and p,p'-DDE (DDE), and a soil artificially contaminated with diesel. In the soil washing experiments, Triton X-100 (TX-100) aqueous solutions were used at different concentrations to obtain wastewaters with different compositions. Removal efficiencies of 66% (DDT), 80% (DDE) and 100% (diesel) were achieved for three sequential washings using a TX-100 solution strength equivalent to 12 times the effective critical micelle concentration of the surfactant (12 CMC(eff)). The wastewater obtained was then treated using a solar photo-Fenton process. After 6h irradiation, 99, 95 and 100% degradation efficiencies were achieved for DDT, DDE and diesel, respectively. In all experiments, the concentration of dissolved organic carbon decreased by at least 95%, indicating that residual concentration of contaminants and/or TX-100 in the wastewater was very low. The co-extraction of metals was also evaluated. Among the metals analyzed (Pb, Cr, Ni, Cu, Cd, Mn and Co), only Cr and Mn were detected in the wastewater at concentrations above the maximum value permitted by current Brazilian legislation. The effective removal of contaminants from soil by the TX-100 washing process, together with the high degradation efficiency of the solar photo-Fenton process, suggests that this procedure could be a useful option for soil remediation.

Photodegradation of sulfamethoxazole in various aqueous media: persistence, toxicity and photoproducts assessment.

The photochemical transformation of sulfamethoxazole (SMX) was investigated in different water matrices: distilled water (DW), distilled water+nitrate (10 and 20 mg L(-1)) and seawater (SW) to evaluate its persistence, toxicity and degradation pathway. A solar simulator Suntest CPS+ was used for the irradiation experiments. Identification of transformation products was performed in DW by liquid chromatography-time of flight-mass spectrometry (LC-TOF-MS). Acute toxicity of irradiated solutions was monitored by Vibrio fischeri and Daphnia magna bioassays in DW. Differences in the degradation rates were observed between DW and SW, being slower in SW. Presence of nitrate (indirect photolysis) in distilled water did not affect SMX degradation rate. No dissolved organic carbon (DOC) removal was observed in any case, thus indicating the formation of abundant transformation products (TPs). Analysis by LC-TOF-MS allowed the identification of up to nine transformation products during photolysis in DW. Only three of them had been previously reported in the literature, detected with other techniques. The cleavage of the sulfonamide bond and the photoisomerization by rearrangement of the isoxazole ring represent the main pathways, at the time that generate the most abundant and persistent intermediates. The acute toxicity of SMX solution varied according to test organisms. Daphnia magna was the most sensitive showing an increase from 60% to 100% immobilization after 30 h of irradiation when depletion of SMX was achieved, thus indicating the higher toxicity of the phototransformation products generated.